Wow!
I think the biggest redstone project I have done was a 6 toggle-button combination lock (for Reoh HQ's main double-doors). It's designed so that the code can easily be changed in no more than a couple seconds.
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Just using switches is a lot less redstone/space BUT when I walk through my main doors the toggle-buttons automatically reset to off and close the doors. Oh and on the inside the same plate opens them back up so I can get out!